It is known that contact lenses can be used to improve vision, and various contact lenses have been commercially produced for many years. Hydrogel contact lenses are very popular today. These lenses are often more comfortable to wear than contact lenses made of hard materials.
One popular contact lens material used for daily and weekly wear is Etafilcon, based on 2-hydroxyethyl methacrylate (HEMA) and a small amount of methacrylic acid. The acidic moiety increases the hydrophilicity of the HEMA material, making a more comfortable lens.
Contact lenses made from silicone hydrogels have been disclosed. Silicone hydrogel contact lenses allow greater amounts of oxygen than conventional lenses (such as HEMA based lenses) through the lens to the eye. However, the silicone materials are not inherently wettable, and coatings and wetting agents have been used to improve the wettability of the lens. Mucin balls are known to develop in the wearer of some silicone hydrogel contact lenses, caused by the shearing force between the eyelid and the material. The long-term effects of this have yet to be discovered.